1. Field of the Invention
The present invention relates to a head gimbal assembly (HGA) with a precise positioning actuator for a head element such as a thin-film magnetic head element or an optical head element, and to a disk drive apparatus with the HGA.
2. Description of the Related Art
In a magnetic disk drive apparatus, thin-film magnetic head elements for writing magnetic information into and/or reading magnetic information from magnetic disks are in general formed on magnetic head sliders flying in operation above the rotating magnetic disks. The sliders are supported at top end sections of suspensions of HGAs, respectively.
Recently, recording and reproducing density along the radial direction or along the track width direction in the magnetic disk (track density) rapidly increase to satisfy the requirement for ever increasing data storage capacities and densities in today's magnetic disk drive apparatus. For advancing the track density, the position control of the magnetic head element with respect to the track in the magnetic disk only by a voice coil motor (VCM) has never achieved enough accuracy.
To solve this problem, an additional actuator mechanism is mounted at a position nearer to the magnetic head slider than the VGM so as to perform fine precise positioning that cannot be achieved by the VCM only. The techniques for achieving precise positioning of the magnetic head are described in, for examples, U.S. Pat. No. 5,745,319 and Japanese patent publication No, 08180623 A.
As an example of such additional actuator, there is a piggy-back structure actuator. This piggy-back structure actuator is formed by piezoelectric material of PZT in an I-character shape with one end section to be fixed to a suspension, the other end section to be fixed to a magnetic head slider and a pillar shaped movable arm connected between these end sections. On the suspension, stepwise stacked are the actuator and the magnetic head slider, namely, the actuator is caught between the suspension and the slider to form a stacked cantilever structure.
However, an HGA with such piggy-back structure actuator will have following various problems:    (1) Because of the stepwise stacked structure, a total thickness of the HGA around the magnetic head slider increases by the thickness of the actuator;    (2) The actuator as a whole consists of piezoelectric material such as PZT of a brittle material, and the actuator and the magnetic head slider are stacked to form a cantilever structure. An impact easily occurs with the moment and also shock resistance is very poor;    (3) Depending upon the size of the magnetic head slider, a travel of the magnetic head element during the precise positioning operation varies. Thus, it is difficult to obtain enough stroke;    (4) Because of three-dimensional and complicated attachment structure of the actuator, the handling at the time of an assembly of the HGA is very difficult and it is impossible to use a conventional HGA assembly equipment causing productivity to be very worse; and    (5) In order not to interfere with the movement of the actuator, it is necessary to assemble with keeping a gap between the actuator and the magnetic head slider and also between the actuator and the suspension. However, forming of such gap will more decrease the shock resistance and it is difficult to precisely keep the gap constant. Particularly, since it is difficult to keep the suspension, the actuator and the magnetic head slider in parallel precisely, the head characteristics deteriorates.
In order to solve the aforementioned problems, inventors of this application have proposed an actuator with a structure in which a head slider is caught in a space between a pair of movable arms capable of displacing in response to a drive signal applied thereto. This structure is not publicly known at the time of filing of this application.
FIG. 1 shows a plane view schematically illustrating the structure of this proposed actuator.
As shown in the figure, the actuator 10 has a rough U-plane shape and consists of a base 11 to be fixed to a suspension and a pair of movable arms 12 and 13 perpendicularly extending from both side ends of the base 11.
At top end sections of the movable arms 12 and 13, formed respectively are slider fixing sections 15 and 16 to be fixed to side surfaces of the magnetic head slider 14. These slider fixing sections 15 and 16 are projected inwardly, namely toward the magnetic head slider 14, so that only these sections 15 and 16 are attached to the side surfaces of the magnetic head slider 14 and that there exists air gaps between the remaining sections of the movable arms 12 and 13 and the side surfaces of the magnetic head slider 14.
The movable arms 12 and 13 consist of arm members 12a and 13a and piezoelectric elements 12b and 13b formed on side surfaces of the arm members 12a and 13a, respectively. The base 11 and the arm members 12a and 13a of the actuator are united by an elastic sintered ceramic.
According to the actuator with such structure, the thickness of the HGA around the magnetic head slider does not increase even if the actuator is attached. Also, since the actuator and the magnetic head slider 14 are not stacked to form a cantilever structure, a shock resistance can be improved. Furthermore, since the magnetic head slider 14 is caught in between the movable arms 12 and 13, it is possible to provide a constant travel to the slider even if the size of the magnetic head slider 14 changes.
However, according to such actuator, since the slider fixing sections 15 and 16 made of the same sintered ceramic were projected inwardly from the surfaces of the movable arms 12 and 13, stress due to applied shock concentrated to corners 15a and 16a at the base of the projections causing these corners to be easily broken. Thus, it was very difficult to greatly improve the shock resistance of the actuator.